The instant invention relates to computers, and more particularly to a routine for a computer in a real-time application.
Real-time applications of computers, i.e., computers monitoring or controlling real world activity of hardware devices, require control of input and output to the computer from each device to regulate the sequencing of computer operation. The computer typically performs numerous tasks for the hardware, one task at a time, but must complete all required tasks within a specified period of time to ensure the necessary servicing of each hardware device. The highest priority function required of the computer is to be performed first and the second priority item second, and so on.
Support of the several running programs requires a sort of "juggling act" where one program runs for a short time, and then control passes to another program that runs for a short while, then on to another program, and so forth. Generally, control is passed when a program delay occurs in the program being performed, or some piece of interface equipment is not available at the moment that it is needed. Conventional process control computer installations have real-time clocks associated with program interrupts, and special features of real-time multiprogramming operating systems to keep the program sequence in order. Computer applications that must keep up with real world activity must compromise between the desired size of least time interval (time quantization) and the size of the computer justifiable in cost terms for the particular installation. For a shorter least time interval checking a greater amount of computer capacity is required, thereby increasing computer overhead, computer capacity not dedicated to function processing. The recursion cycle of conventional systems is on the order of 1/4 to 1/2 second. Attempts to reduce this recursion cycle to much shorter times increase the computational load on the computer and eventually saturate it, by requiring the computer to recycle through all of the simultaneously-running programs during each recursion cycle. To control real time applications, prior art computers have devoted as much as a third of their processing capability to keeping track of time intervals. This dedication of computer processing capability to time keeping limits computer utilization, and wastes computer computation capability.
Accordingly, an object of the instant invention is to provide a routine timer outside the computer mainframe for controlling simultaneously-running delays and timers for a plurality of programs, so that the processing capability of the computer is increased without losing coordination of the processes being handled by the computer.